An aircraft pilot needs up to date (timely) information on weather conditions in order to avoid flying through severe weather conditions. Typically, this is provided by displaying weather conditions detected by an airborne weather radar. The weather radar system includes an antenna receiver/transmitter unit attached to the aircraft. The unit emits a concentrated beam of microwave energy. The returned echo indicates the intensity of detected targets. The detected intensity is displayed as color coded targets depicting echoes on a display (i.e. cockpit monitor). The intensity of the rainfall at a given location is indicated by the color displayed. For example, black represents very light or no precipitation, green represents light precipitation, yellow represents moderate precipitation, red represents heavy precipitation and magenta represents very heavy precipitation.
The airborne weather radar cannot be relied upon at increased distances from the sensor because a radar beam increases in width with increased distance from the sensor. At a large distance the beam is very wide, sometimes on the order of tens of miles. The radar sensor detects a target at a particular distance based on the average intensity of the echo across the full beam width. A typical thunderstorm is only one mile in diameter. Thus, a storm detected within a beam that is 10 miles wide may only return an echo indicating one-tenth the intensity because of intensity averaging over the full beam width. Thus, the intensity is incorrectly represented as green (light storm) instead of showing regions of red (heavy storm). The returned echo is misleading because it does not depict the real intensity of the weather ahead of the aircraft.
Weather providers provide more accurate and detailed images of weather conditions than can be derived from airborne weather radar. Systems for downlinking these images from satellites, for display on monitors in the cockpits of aircraft are available. For example, the Orbcomm network provides a request/reply service, which downloads from a satellite the latest weather uploaded from a ground station to the satellite in reply to a request. However, weather graphics files are very large and a link to the aircraft cockpit from a satellite is slow. Thus, it takes a long time to download the weather conditions from the satellite. For example, the bandwidth of a link from a satellite in the Orbcomm network of Orbital Sciences satellites is 4800 bits per second (bps).
Typically, the minimum data to reconstruct an image is downlinked to minimize the bandwidth. This results in a very low-resolution image comprising a series of linked blocks, which does not accurately represent the shapes of weather features.